The present invention relates to a lens apparatus of a so-called collapsible type which is mounted on an image-pickup apparatus such as a digital still camera.
A lens apparatus of the collapsible type having a zooming ratio of 2 to 3 typically employs a two-stage telescopic structure in which a so-called moving cam ring and a first barrel for holding a first lens closest to an object are moved in the direction of an optical axis relative to a fixed barrel which is secured to a camera body. For example, Japanese Patent Laid-Open No. 2001-324663 has disclosed a structure in which a moving cam ring is driven along a cam groove portion formed in a fixed barrel, and a first barrel (first lens) and a second barrel (second lens) serving as a variator and placed on the image plane side of the first barrel are driven along a cam groove portion formed in the moving cam ring.
The moving ranges of the first barrel and second barrel in the lens apparatus arranged as described above depend on the lengths of the fixed barrel and the moving cam ring. As the zooming ratio is higher, the moving ranges of the first barrel and second barrel need to be wider.
In recent years, cameras require not only a reduced size but also an increased magnification. However, it is difficult to increase the moving ranges of the first barrel and second barrel by means of the moving cam ring which has the limited length in the optical axis direction in the abovementioned two-stage telescopic structure.
To address this, some proposals have been made of cameras provided with lens apparatuses of a three-stage telescopic structure. For example, Japanese Patent Laid-Open No. 2004-085932 has disclosed a lens apparatus of such a three-stage telescopic structure in which a second barrel switches between two cam groove portions formed in a moving cam ring to realize a wider moving range of the second barrel.
Japanese Patent Laid-Open No. 2004-325555 has disclosed a lens apparatus of the two-stage telescopic structure which is intended to widen the moving range of a lens. In the lens apparatus, a motor is placed on a second barrel and the rotation force of the motor is transmitted to a lead screw via a gear train. The lead screw engages with a nut placed on a third barrel disposed closer to an image plane than the second barrel. The lead screw is rotated to move the third barrel in the direction of an optical axis relative to the second barrel which is movable in the optical axis direction, thereby widening the moving range of the third barrel.
In the lens apparatus disclosed in Japanese Patent Laid-Open No. 2004-085932, some play is intentionally provided between three cam followers formed on the second barrel and the associated three cam groove portions in order to achieve smooth switch of the second barrel between the cam grooves. The play is likely to cause large decentering of the second barrel depending on the posture of the camera.
To reduce the decentering, it is possible to use an alignment mechanism for biasing the second barrel toward one side in the diameter direction by a movable cam follower provided with a spring. However, when the alignment mechanism is provided and the barrel switches between the cam groove portions, some problems easily occur such as unsmooth telescopic operation since the movable cam follower gets snagged when it comes off one cam groove portion and then is engaged with the other cam groove portion.
The structure disclosed in Japanese Patent Laid-Open No. 2004-325555 is effective in widening the moving range of the third barrel as a focus lens. However, the structure is not provided for widening the moving range of the second barrel as a variator, that is, for realizing a higher magnification.